The present invention is directed to processes for hydrophilizing surfaces of fluidic components and systems.
Modern analytical systems for determining physical or chemical parameters of a liquid often have complex fluidic systems which have to ensure that the liquid to be examined is transported substantially without interference and carry-over to the sensory elements and that the liquid sample is transported away from the sensory elements after determining the parameters.
Such analytical systems are used in particular in clinical diagnostics where they are used especially for blood gas analysis or for other measurements of samples present in a liquid form. Such systems are used for example to determine the oxygen or carbon dioxide partial pressure of blood, haemoglobin parameters such as total haemoglobin, oxyhaemoglobin, carboxyhaemoglobin or methaemoglobin of whole blood or haemolysed blood, the haematocrit value of whole blood as well as the pH value or the concentration of ions such as lithium, sodium, potassium, magnesium, calcium or chloride or special metabolites such as glucose, urea, creatinine or lactate in physiological liquids. Such complex analytical systems often have different sensory elements to determine the respective parameters which are used for many determinations. Such sensory elements are for example electrochemical or optical sensors for determining the gas values, the pH value, the ion values and the metabolite values or the optical measuring devices for determining the haemoglobin values.
In addition to such systems, systems are also known which can be used in the direct vicinity of the patient and in which the liquid sample is transferred directly from the patient into the analytical system by means of a tube system.
In addition to fluidic partial systems for transporting the sample liquid and/or quality control media, many analytical systems often also contain other fluidic partial systems in order to, for example, transport liquid or even gaseous calibration media and/or wash or cleaning media from storage containers to the sensory elements and from there to waste containers. The transport of the various media is controlled by pumps and valves along paths that differ in parts.
Such modern instruments often use very small amounts of sample and liquid that are often aliquoted again in the fluidic system. Depending on the number and type of parameters to be determined, the required sample volume can for example be between about 50 and about 120 microliters. However, special measures are required to ensure that such small sample volumes are transported without contamination to the sensory elements of the analytical system. Contamination can for example be caused by residues of the previous samples or of control, calibration, or cleaning media remaining in the fluidic system. In order to avoid such contamination, washing and drying steps can for example be inserted between the individual determinations of the measured values.
In the case of sensory elements for determining gases such as electrochemical or optical gas sensors, but also in the case of optical measuring systems for example to determine haemoglobin, there is still a risk that measurement errors occur due to the inclusion of gas bubbles in the fluidic system, especially in the area of the sensory elements. Thus when gaseous analytes are determined in liquids by means of electrochemical gas sensors, problems can occur in the sample measurement or in the calibration or quality control when the sample or the quality control or calibration agent does not completely fill the liquid-conveying area of the sensory element or when there are gas bubbles such as air bubbles in this area. Gas bubbles form especially when non-uniform inner surfaces are present within the fluidic system which have different wetting properties for liquids. Gas bubbles are formed or become attached especially frequently at sites in the fluidic system at which there is a sudden transition in the wetting properties of the inner surfaces of the various fluidic components. This is, for example, the case when surfaces made of different materials abut one another. However, the fluidic systems of many analytical systems consist of many individual fluidic components made of different materials which have abutting surfaces with different wetting properties. Furthermore, many of the fluidic components of such analytical systems are made of plastics which are characterized by a low hydrophilicity and a hydrophobicity. Such plastic surfaces are poorly wetted with aqueous liquids and have a particular tendency to form or attach gas bubbles.